The objective of this study is to elucidate the intracellular interactions of the HIV regulatory protein Nef with host cell activities. Early in the HIV-1 infective process this retrovirus expresses regulatory proteins, with the Nef transcript representing nearly 80% of total viral mRNA. In vivo infectivity by the closely related simian form of HIV is achieved in the absence of Nef expression, but there is an absolute requirement for Nef in the development of the immunodeficiency. This essential activity of the Nef protein in the development of AIDS has not been defined. We have recently established that the Nef protein associates with a member of the p21-activated kinase (PAK) family, which is known to initiate activation pathways in those cells which can be infected by the HIV virus. In the periphery, these cells include T cells and macrophages, and in the CNS, brain macrophages and to a lesser degree astrocytes. We had previously found that Nef expression independently caused enhancement of T cell activation and modulation of the CD4 molecule, the HIV receptor. The effect of expression of this pathogenic regulatory protein on macrophage/glia cell function will be examined. The biochemical mechanism for these Nef-mediated alterations in both T cells and macrophages and the nature of the Nef-PAK association will be defined.